1. Field of the Invention
This invention relates to a method for the production of integral silicone molded products comprising a unitary structure of a substrate with a coating having different phases and the integral silicone molded products prepared therefrom. More specifically, this invention relates to a method for the production of integral silicone molded products characterized by coating a substrate with a polyorganosiloxane composition which is curable by the addition-reaction of alkenyl radicals with silicon-bonded hydrogen atoms and curing to produce a unitary structure having different phases.
2. Description of the Prior Art
In general, polyorganosiloxanes cured by the addition reaction of silicon-bonded lower alkenyl radicals to silicon-bonded hydrogen atoms exhibit excellent properties compared to organic resins. In particular, they possess excellent thermal resistance, cold resistance, and weather resistance and thus exhibit excellent long-term electrical properties such as stable electrical insulating properties and stable dielectric properties over a wide range of temperatures from low to high temperatures. They also exhibit excellent mechanical properties such as a stable strength, elongation, elasticity, and stress relaxation effect. It is also known that the above- mentioned excellent electrical and mechanical properties are little degraded by long-term ultraviolet irradiation. Moreover, silicone compositions are usually nonflammable or flame retarding. Furthermore, such silicone compositions may be converted relatively easily into a liquid, gel, elastomer, or hard resin without adversely affecting the essential properties of the silicone.
Silicones are used in many applications in various industries because they exhibit the above-mentioned excellent properties. For example, in the electrical industry, silicones are used for filling, impregnating, coating, and adhering electric and electronic parts because of their excellent insulating properties and nonflammability. Silicones are also widely used as a stress relaxing material or sealant for semiconductor elements, glasses, or polymers and as insulating protective materials for electric wire or cable because their mechanical and electrical properties are stable over a wide temperature range. In the machine industry, silicones are used as a vibration or impact absorber due to their excellent elasticity while in the building construction industry silicones are widely used as sealants, caulking materials, and paint.
Although silicone compositions exhibit the above-mentioned excellent properties, they exhibit the following disadvantages. For example, a liquid silicone which has been impregnated or filled as an insulating material will leak from the case or mix with dust due to its fluidity. A gel or elastomeric cured material may be used as a protective material for substrate with a low mechanical impact strength or thermal shock resistance based on its excellent adhesion, adhesiveness, resistance to moisture invasion, corrosion inhibition, and stress relaxing effect; however, the silicone may suffer from dust adhesion with resulting problems with the properties and external appearance. Moreover, the surface of a gel or elastomeric cured product does not possess sufficient mechanical strength, e.g., friction resistance and tear strength. On the other hand, compared with the above-mentioned liquid, gel, or elastomeric cured products, hard resinous cured products are superior in their suppression of fluid leaks and dust adhesion and have superior mechanical strength; however, they exhibit high hardness and a high modulus of elasticity with the result that they cannot satisfactorily exhibit stress relaxing effects for mechanical impact or thermal shock.
Methods for improving the above-mentioned defects in the silicone compositions have been used. Examples of these methods are as follows.
(A) A case or cover of inorganic or organic material is used for a liquid, gel, or elastomeric cured product in order to prevent fluid leaks or dust adhesion or for mechanical protection.
(B) A protective layer of another hard organic material is applied on the liquid, gel or elastomeric cured product in order to suppress dust adhesion or for mechanical protection.
(C) Romenesko in U.S. Pat. No. 4,163,082, issued July 31, 1979, describes coating a silicone gel or grease with a UV curable organopolysiloxane to reduce the surface tack and therefor reduce the dust adhesion. The UV curable coating composition is a mixture of an organopolysiloxane having an average of at least two olefinic radicals per molecule and a hydrogen-containing organopolysiloxane.
However, method (A) exhibits the disadvantages of increasing the number of processes, placing limitations on shape, and increasing the cost of starting materials. Method (B) exhibits the disadvantages of insufficient interlayer bonding strength resulting in the ready occurrence of interlayer peeling, increasing the number of processes, and increasing the cost of starting materials. Method (C) exhibits the disadvantages of ready occurrence of interlayer peeling as in method (B) and a complicated process control such as the control of film thickness. In particular, the film thickness is difficult to control when the final cured product is very thin such as several tens of .mu.m.